Dmytro Firtash, Ukraine oligarch, protests innocence

In a scene reminiscent of the Cold War, police in Vienna sealed off a small, quiet street in the city centre one night in March, before surrounding an East European businessman as he came out of his office.

"It was a real shock. I came here for two days from Paris and was due to fly to London the next morning," Mr Firtash told the BBC, in his first interview with an international broadcaster.

"There is a Russian proverb that you should be wary of two things: extreme wealth and prison."

Dmytro Firtash (R) with the BBC's Richard Galpin in the spot in Vienna where he was was arrested by Austrian police at the behest of the FBI
Mr Firtash is a donor to Cambridge University in the UK, which launched its Department of Slavonic Studies with his support

A Vienna court set bail at 125m euros ($173m; £102m), a record for Austria and possibly globally.

But in a matter of days the money was deposited with the court and Mr Firtash was driven away from the detention centre in his armoured Mercedes.

Although he escaped his prison cell, he has not been able to return home to Ukraine. According to his bail conditions, he must remain in Austria.

So now he spends his time in and around the Austrian capital, awaiting the outcome of the extradition hearings.

Battle of his life

His days, he says, are divided into three parts: continuing to run his vast business empire in Ukraine remotely from Vienna; trying to play a role in stabilising his crisis-ridden home country; and finally, meeting his lawyers and advisers to discuss the extradition proceedings.

We met him at the same office from which he had walked into the arms of the Austrian police back in March.

We talked for almost two hours and were interrupted only once, when we became aware of strange noises emanating from the long window sills.

One of Mr Firtash's thick-set bodyguards lumbered over, opened the windows and removed two small boxes which had been placed there deliberately.

They were special devices creating the muffled sound of background "chatter" to prevent anyone eavesdropping on our conversation.

"We want to make sure this interview really is just for you," joked one of the cluster of public relations consultants, advisers and business colleagues who sat in the room throughout the interview.

It was a touch paranoid, but there is little doubt Mr Firtash is now in the battle of his life.

According to the US Department of Justice, the FBI has been investigating Mr Firtash for eight years, culminating in the drawing up of charges in 2013.

Mr Firtash (R) was seen as a key backer of Viktor Yanukovych during his presidency

He is accused of leading a criminal organisation allegedly involved in bribery and corruption while trying to win a foreign business contract.

The Justice Department alleges that at least $18.5m (£11m) was transferred via US financial institutions to be used as bribes.

"I am absolutely innocent, I did not pay any bribes and no organised criminal group was set up," says Mr Firtash in response.

He insists his arrest is illegal and that the US has fallen for disinformation about him supplied by his enemies in Ukraine.

Tensions

But Mr Firtash is no stranger to controversy.

He has been accused of having links with the East European mafia, which he strongly denies.

And there have been many questions about a gas trading company which he set up with the Russian energy giant Gazprom to act as an intermediary in the sale of gas to Ukraine.

What is beyond doubt is that he has strong business connections with Russia. This may be the main reason for his arrest on 12 March, almost a year after the US Department of Justice drew up the charges against him.

His arrest came days before the referendum in Crimea, on leaving Ukraine to join Russia. Tensions between Moscow and the West were rapidly rising to Cold War levels.

Mr Firtash is wanted by the US in part because of his strong business links with the elite in Russia, about whom he may have much sensitive information

Mr Firtash believes he is an early casualty of this new East-West conflict.

"There's a geo-political struggle between the United States and Russia underway. The United States needs an enemy abroad to solve problems at home. And Ukraine happened to become a battlefield," he says.

A well-placed source in the US also told the BBC he believes Mr Firtash may have been picked up because of his links with Russia and because of his support for the now ousted Ukrainian President Viktor Yanukovych.

"He knows a whole lot of things about the elites in Russia and Ukraine," the source said.

And that highly sensitive information is something the US authorities could try to get from Mr Firtash if he is extradited.